1. Field of the Invention
This invention relates to a method of manufacturing an electron-emitting device and an image-forming apparatus comprising such devices as electron sources. More particularly, it discloses a novel method of manufacturing a surface conduction electron-emitting device which is categorized as a cold cathode type electron-emitting device.
2. Related Background Art
There have been known two types of electron-emitting device; the thermoelectron type and the cold cathode type. Of these, the cold cathode type include the field emission type, the metal/insulation layer/metal type and the surface conduction type.
A surface conduction electron-emitting device is realized by utilizing the phenomenon that electrons are emitted out of a small thin film formed on a substrate when an electric current is forced to flow in parallel with the film surface. A surface conduction electron-emitting device is typically prepared by arranging a pair of device electrodes on an insulating substrate and an electrically conductive thin film, which may be a metal oxide film, between the electrodes to electrically connect them (hereinafter referred to as "thin film for forming an electron-emitting region") and subjecting the thin film to an electrically energizing process referred to as "electric forning" to locally destroy the this film and produce therein an electron-emitting region. The thin film is in fact a film consisting of fine particles of a metal oxide before and after the electric forming operation. Hereinafter, a thin film having an area for forming an electron-emitting region is simply referred to as a thin film including an electron-emitting region.
An electron-emitting device is a so-called non-linear device that shows a sudden and sharp increase in the emission current Ie when the voltage applied thereto exceeds a certain level (a threshold voltage), whereas the emission current is practically undetectable when the applied voltage is found lower than the threshold. Because of this remarkable feature, an image-forming apparatus can be realized by using an electron source comprising a plurality of surface conduction electron-emitting devices and a fluorescent body that emits visible light when irradiated with electrons emitted from the electron source.
materials that can be used for a thin film including an electron-emitting region include, besides metal oxides, metal and carbon. When a metal or metal oxide is used, an organic metal compound is applied to the substrate to form a thin film of the compound and then baked to produce a thin metal oxide film. Massive efforts are currently being made to fully exploit the potential of this method because it involves a relatively simple manufacturing process and can be used to prepare an image-forming apparatus having a large display screen.
FIGS. 11A through 11K of the accompanying drawings schematically illustrate steps of manufacturing an electron-emitting device using a conventional method. Note that Steps a through k described below correspond to illustrations FIGS. 11A through 11K respectively.
Step a: Electrodes 5 and 6 are formed on an insulating substrate 1.
Step b: A film of a selected material such as Cr is formed on the entire surface of the substrate 1.
Step c: Resist is applied on the entire surface of the film formed in step b.
Step d: The applied resist is exposed to light, using a photo-mask having a pattern for a thin film including an electron-emitting region to be formed there.
Step e: The resist is photographically developed.
Step f: The Cr of the areas not covered by the resist is removed by etching, using an acidic etchant.
Step g: The remaining resist is removed by means of an organic solvent.
Step h: An organic metal compound solution is applied to the product of Step g by using an appropriate means such as a spinner to form an organic metal thin film 7.
Step i: The organic metal compound thin film 7 is turned into a metal oxide thin film as it is baked in a furnace at 300.degree. C. for about 10 minutes.
Step j: A thin film 2 for forming an electron-emitting region is formed to conform to an intended pattern by removing the remaining Cr by means of a lift-off method.
Step k: An electron-emitting region 3 is produced by means of an electric forming process.
However, the above described known method involving a baking process is accompanied by a problem that it cannot rigorously control the thickness of the thin film including an electron-emitting region and can produce thin films with different thicknesses.
Thus, with this known method, electron-emitting devices can operate with varied performances for electron emission so that an image-forming apparatus realized by using an electron source comprising such electron-emitting devices can be poorly adapted for high definition image display because of the varied and unstable performances of the electron-emitting devices.
Additionally, since the entire surface of the thin film of the organic metal compound is baked by the above described known method, it requires the use of a photolithography or dry etching technique for the patterning operation to makes the entire process rather cumbersome. Particularly, it is extremely difficult using this method to realize a large display screen by two-dimensionally arranging a large number of electron-emitting devices.